High Intensity Interval Training

High Intensity Interval Training (HIIT): exercising at very high intensity interspersed with periods of moderate rest

High-intensity interval training (HIIT) is a growing method of exercise. Research suggests that implementing HIIT into your exercise regimen will improve your health, boost weight and fat loss, promote human growth hormone production, and improve strength and stamina. HIIT is an incredibly short and effective method for improving fitness, but is also extremely taxing on the body, therefore it is not recommended for everyone.

To understand how HIIT is effective, it may be helpful to understand bioenergetics. Bioenergetics is the flow of energy in a biological system; or the conversion of macronutrients (fat, protein, and carbohydrates) into biologically usable forms of energy.

Intensity and Duration of Exercise are Inversely Related

That is, as the intensity of exercise increases, the duration of exercise decreases. Short-term, high-intensity activities receive a greater contribution of energy from the anaerobic (without oxygen) energy systems, however the body cannot survive without adequate levels of oxygen. When engaged in long-term, low to moderate-intensity exercise, the majority of energy is supplied from aerobic (with oxygen) sources, allowing the human body capable of running marathons.

Influence on Health

Researchers have observed the effect of a 12-week HIIT intervention on total body, abdominal, trunk, visceral fat mass, and fat free mass of 46 young overweight males - some of which were randomly assigned to either exercise or control group. The exercise group implemented HIIT three times per week, 20 min per session, for 12 weeks. Overall, after the 12 week of HIIT, the exercising group resulted in significantly improved aerobic power (by 15%), significant weight loss (1.5 kg), significantly reduced total fat mass (2 kg), significantly reduced adipose tissue of the abdomen and trunk (0.1 kg and 1.5 kg), significantly reduced visceral fat (17%), significantly increased lean body mass for the leg (0.4 kg) and for the trunk (0.7 kg) (Heydari, Freund, & Boutcher, 2012).

Another group of researchers implemented a HIIT program consisting of a total of six training sessions of 10, 1 minute cycles of high intensity cycling (~60% peak power), followed by 1 min of recovery between intervals. The researchers observed that the HIIT program increased muscle oxidative capacity (∼35%), improved blood sugar regulation (~260%) and insulin sensitivity (∼35%) ﻿(Hood, Little, Tarnopolsky, Myslik, & Gibala, 2011)﻿.

Researchers have also observed significantly improved insulin sensitivity and blood sugar regulation among individuals with type-2 diabetes that implemented just ONE HIIT session of 10 cycles of 60 seconds of high intensity, interspersed with 60 seconds rest (Gillen et al., 2012).

Recommended HIIT Protocols

Tabata method

Created by Izumi Tabatam, the Tabata method consists of high intensity sprints at about 170% of VO2 max. Sprints should be 20 seconds at a high intensity, followed by a 10 second rest for a total of 8 cycles. Total workout time: 4 minutes. Recommended for those are extremely fit with little available time 2-4x per week.

Little Method

Created by Johnathan Little and Martin Gibala, the little method is composed of 60 seconds of high-intensity exercise, about 95% of VO2 max (high oxygen consumption), with 75 seconds of low intensity or active rest. Workout should conclude after 12 cycles (about 27 minutes). Recommended for the intermediate 3x per week.